Responding To The Sister Complex
by k0dokuna
Summary: Hiromi Nase has always had a thing for little sisters, and his actual little sister, Mitsuki, has always deemed them as perverted and creepy. However, Mitsuki begins to have erotic dreams about her brother and begins to fantasize. Read more as Mitsuki Nase begins to respond to the sister complex. Warning: smut, incest, 18 . Mitsuki Nase x Hiromi Nase.
1. Chapter 1

Mitsuki Nase x Hiromi Nase

Notice: I do not own Beyond the Boundary or any of the characters affiliated with the anime.

Warning: contains some smut/explicit scenes. 18+

* * *

Mitsuki unwrapped another sucker from her pocket and began sucking on it while sorting through the books in the club room. All of a sudden, she felt a soft scarf being wrapped around her bare neck and a cold breath hit her shoulder, causing her to shiver.

"Hello, my Mitsuki," a voice said.

She turned around to see her brother, Hiromi, standing there with his hands in his pockets, looking at her expectantly.

"Baka," She muttered under her breath, attempting to walk around her onii-chan.

Hiromi stopped her with his hand and shoved her back a step. "Where do you think you're going, Mitsuki-chan?" He asked with a lick of his lips.

Mitsuki dropped her sucker suddenly, causing it to fall to the floor and roll underneath one of the bookshelves.

"Tsk, tsk, my little onee-chan." Hiromi teased, lifting up Mitsuki's chin with two fingers. "Looks like I'll have to give you something else to suck on."

Mitsuki awoke, shooting up in her bed, gasping for breath. _Why am I having these disgusting dreams?_ She thought to herself. For the past couple weeks she had been dreaming about Hiromi like this every night. The only logical explanation she could think of was that his dreams were somehow transferring to her head through the bedroom walls.

"What's the matter, Mitsuki?" Kuriyama-san questioned her. They were sitting in the club room, just the two of them, waiting for the boys, and Kuriyama Mirai noticed that Mitsuki was hardly talking. She seemed distracted by something, a thought in the back of her mind, perhaps?

Mitsuki blinked and popped the sucker out of her mouth, getting ready to respond, when the club room's door swung open with a bang. Hiromi and Akihito Kanbara stood there side by side with proud smiles on their faces.

"We've come to welcome a new guest to the Literary Club," Akihito announced, putting one hand on his hip and running another through his hair proudly.

"Oh boy," Mitsuki muttered quietly, bracing herself for yet another perverted male to enter the room.

However, when the two boys stepped aside, Mitsuki was greatly surprised to see a short girl standing there, her hands behind her back, her cheeks red beyond belief.

"Meet Nakamura Momo-san!" Hiromi and Akihito announced proudly, their arms spread wide.

"H-Hi," Momo-san stuttered, looking down at the floor shyly.

Mitsuki and Kuriyama-san sat there in awe, unable to form words. The silence was awkward and uncomfortable, forcing Akihito to speak. "Don't be so afraid guys. Hiromi and I found her wandering around and asked her to join the group and she said yes! Now you girls can make more female friends!"

Mitsuki sighed and popped the sucker back into her mouth, annoyed. Who said she needed to make more _female_ friends? Who said she needed to even make more friends at all? She had become friends with Kuriyama-san and that was nearly enough.

Momo-san took a seat next to Kuriyama-san and looked around the club room happily. "I've always wanted to be a part of a Literary Club! I love to read. I don't have many friends around here since I just moved, so books have been my friends." She laughed uneasily, her cheeks blushing once more. She had caramel-brown hair that was pin straight, but appeared soft and lush. She had an abundance of freckles upon her round cheeks and a pair of blue-framed glasses sat on the bridge of her button nose.

"Well," Mitsuki spoke, looking up at her brother and Akihito. "I can certainly tell why you asked her to join."

Kuriyama-san nodded her head in agreement. Hiromi continued to smile and said, "She's the perfect little sister."

"Plus," Akihito chimed in. "She wears the cutest little frames!" His eyes sparkled and he moved up next to Momo, rubbing his cheek against hers.

"Pervert!" Mitsuki shouted, throwing books at Akihito.

"Ow, ow, ow!" Akihito responded, rubbing his head. "She's just so kawaii."

Hiromi stepped up behind Akihito, gently placing his hands on his warm waist. "I agree. She could teach you two a few things."

"Are you even a real little sister?" Mitsuki snapped, narrowing her eyes at Momo.

"Well-"

"Jealous, are we?" Hiromi stepped in, a sly grin on his face.

"Tsk." Mitsuki blushed and looked away. _This is enough for today. _She stood up abruptly, threw her sucker in the trash, and walked out of the club room, heading for home.

* * *

AN: Hello! This is my first fanfic I have ever written and posted. Reviews and ratings would be great! I realise we're not that far into the story yet, but things will quickly escalate within the next couple chapters. I plan to keep this a short fanfic with some smut and maybe a little fluff. Let me know how I'm doing and thank you for reading! XOXO


	2. Chapter 2

Mitsuki Nase x Hiromi Nase

Notice: I do not own Beyond the Boundary or any of the characters affiliated with the anime.

Warning: contains some smut/explicit scenes. 18+

* * *

It was a couple days since Nakamura Momo-san had joined the Literary Club. Mitsuki was still having embarrassingly erotic dreams about Hiromi. She chose to ignore them as best she could, not wanting to admit that maybe there really was a reason behind these dreams of hers.

"It's bad to have sweets before breakfast, you know," Hiromi informed his little onee-chan as he flipped the pancakes on the griddle.

Mitsuki ignored him and continued with her sucker in her mouth, looking out the window, admiring the dazzle of the sun upon the sidewalk and the trees. Summer break would be coming up in several weeks and there was nothing the Nase siblings wanted more at the moment.

"Don't worry," Hiromi smiled, noticing the longing look in Mitsuki's eyes. "Summer break will come before you know it and the Literary Club can do something together, just like old times."

Hiromi set a plate of pancakes down before Mitsuki. "I need a fork, Baka." Mitsuki muttered, sitting up straighter and crossing her legs.

Hiromi handed her a fork, his rough hands brushing against Mitsuki's soft ones. A tingle went down her spine and she yelped suddenly. "What is it?" Hiromi asked, worried. "I didn't hurt you, did I?"

All Mitsuki could think of was the dream she had the night before…

"Come on, it's just a little further," Hiromi pestered, grabbing ahold of her soft arm and dragging her faster.

"B-But," Mitsuki spoke, out of breath from their hike through the woods. "We've been walking for miles!"

"There it is!" Hiromi pointed proudly. A large tree house was built atop a towering tree, built with great care. "It's the one I was telling you about! Come on."

Hiromi continued to drag Mitsuki along until they finally reached the rope swing that would bring them to the entrance of the tree house. "You go first, just in case you fall," Hiromi ordered.

Mitsuki did as she was told, aware that Hiromi could probably see her panties, but said nothing about it.

When Mitsuki entered the tree house, she realised how tiny it really was. From the ground it seemed large and important, powerful even. There was a soft green rug laid down on the floor and unlit candles scattered around. Rainbow beads hung from the windows of the treehouse, causing the room to light up, the sun bouncing off of the glass beads, making the room appear glittery and bright.

"Woooow," Mitsuki said quietly, afraid that if she were too loud that the beauty would somehow fade.

"Amazing, isn't it?" Hiromi said behind her, his breath hitting her long, thin locks. "I wanted to show this to you. You're the only one that knows about it."

Mitsuki gulped uneasily, turning around to look at her brother, backing up a little. "Why's that?" She tried to add an indifferent attitude to her words, but it came out softer than she had intended.

"Because," Hiromi answered, a sly grin plastered on his face, eyelids drowsy. "You're special to me." He advanced towards Mitsuki slowly, causing her to back up.

"Oh," Mitsuki said, embarrassed as she realised she had backed all the way up to the back wall of the tree house.

Hiromi towered over her, his breath heavy, his eyes filled with an _evil_ lust. "Your lips look so kissable," He admired, placing a long finger on her delicate bottom lip.

"S-Stop messing around!" Mitsuki ordered, pounding her fists on her big brother's chest helplessly.

"Oh, we're feeling naughty, are we?" Hiromi smirked. He spun Mitsuki around, shoving her closer to the wall. He lifted up her skirt and his hand lingered down between her plump, shaking thighs. He teased around the edges of her pussy, where it was fleshiest.

"Mm!" Mitsuki whimpered. She quickly covered her mouth in surprise, blushing profoundly. Had she really just made that reaction to such a perverted touch?

"Hm," Hiromi admired. "You like that, huh?" He tucked her hair behind her right ear and began to lick and nibble while his fingers teased her more.

"S-Stop!" Mitsuki pleaded, holding in moans. Her legs were shaking and her vision became hazed.

Hiromi gently pushed his middle finger into Mitsuki's soft pussy, taking note of how wet she was. He stuck in another finger and began to move them in and out, in and out, faster and faster.

"Ahh!" Mitsuki moaned, blushing and ashamed. "N-Not like that, Hiromi!"

"But I think your pussy likes it," Hiromi said, pulling out his fingers and showing his sister the goo that dripped from them. "You're so sensitive, Mitsuki."

"B-Baka!" Mitsuki whimpered as Hiromi began fingering her once more. "We're not supposed to do this! We're siblings!"

"That's right, Mitsuki," Hiromi cooed. "We're siblings. And you're my kawaii little onee-chan." Hiromi shoved in a third finger, moving quicker and deeper.

"H-Hiromi!" Mitsuki yelped, her knees beginning to buckle, her cheek pressed against the wall of the treehouse. Everything seemed so hot and claustrophobic all of a sudden and Mitsuki just wanted to be let free. "Let me cum!"

"Not unless you say it," Hiromi growled with a grin, slowing his fingers down.

"S-Say what?"

"Oh," He purred mischievously. "You know what."

All of a sudden, Mitsuki felt Hiromi's other arm wrap around her, diving into her panties along with the other. A finger found her clitoris and began teasing and flicking it.

_"Oniiii-chaaaaan!"_

"Hellooo!" Hiromi said, waving his hands in front of Mitsuki, trying to get her attention.

Mitsuki snapped back into the present, her cheeks full of colour, and her breathing heavy. "I-I'm sorry," She apologized, putting her sucker in her mouth and sucking once again.

"It's okay…" Hiromi trailed off somewhat awkwardly. "Just eat your pancakes. And give me this."

Hiromi snatched up Mitsuki's sucker and popped it into his mouth, sucking cheerfully.

"H-Hiromi…" Mitsuki whined, embarrassed. She squeezed her legs together, feeling a tingling between them.

"Hmm?" Hiromi asked innocently.

"But, my germs-"

"It's okay. We're siblings."

Mitsuki nodded, beginning to eat her pancakes.

"And you're my little onee-chan," Hiromi purred, giving her a kiss on the cheek and walking away, one hand in his pocket, the other attached to the stick of the sucker in his mouth.

* * *

AN: Eee! Not much, really, just some more looks into Mitsuki's dreams, hehe. Thank you to the people that viewed my story and left reviews, favourited, or followed! You inspired me to write another chapter so quickly, so I hope it satisfies you guys. Continue leaving me comments and such! XOXO


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